The invention relates to calculator or digital data processing systems, and particularly to an improved MOS/LSI semiconductor chip for use in such systems.
Electronic calculator systems of the type having all of the main electronic functions within a single large scale integrated (LSI) semiconductor chip, or a small number of chips, are described in the following prior applications or patents assigned to Texas Instruments Incorporated: U.S. Pat. No. 3,819,921, by Kilby et al, for "Miniature Electronic Calculator", based on an application originally filed Sept. 29, 1967; Ser. No. 163,565, filed July 19, 1971 by Boone and Cochran, for "Variable Function Programmed Calculator" (refiled as Ser. No. 420,999 on Dec. 3, 1973) issued as U.S. Pat. No. 4,074,351; Ser. No. 400,473, filed Sept. 24, 1973, by Bryant for "Digit Mask Logic In Electronic Calculator Chip" now U.S. Pat. No. 3,892,957 issued July 1, 1975; Ser. No. 400,437, filed Sept. 24, 1973, by Vandierendonck, Fisher and Hartsell for "Electronic Calculator With Display And Keyboard Scanning" now U.S. Pat. No. 3,900,722 issued Aug. 19, 1975; Ser. No. 397,060, filed Sept. 13, 1973 by Cochran and Grant, for "Multi-Chip Calculator System" now U.S. Pat. No. 3,900,722; and others.
These prior inventions have made possible vast reductions in cost and size, and increases in functions, in electronic calculators. Many millions of such calculators have been produced. The efforts to reduce manufacturing costs and increase the functions available to the user are continuing. Particularly, it is desirable to provide a basic chip structure that is quite versatile and can be used for many different types of calculators and similar digital processing equipment. This permits a single manufacturing facility to produce large quantities of the same devices, differing only in a single mask change, to produce dozens of different variations, while still maintaining large volume cost advantages.
The previous MOS/LSI calculator chips as referred to above were generally register organized in that a single instruction word operated on all of the digits in a given register. A more versatile approach is to make the machine "digit organized", operating on one digit at a time. For example, it may be desired to test or set a particular one bit flag. In a register machine an entire thirteen digit register must be addressed and masked to implement this, whereas a digit organized machine may access only the needed digit or bit. An example of a calculator chip of such nature is referred to at pages 31-32 of "Electronics", Sept. 25, 1972, by Rockwell.